Polycrystalline diamond compact (“PDC”) cutters have been used in industrial applications including rock drilling and metal machining for many years. Generally, a compact of polycrystalline diamond (“PCD”) or other superhard material is bonded to a substrate material, e.g., a sintered metal-carbide, such as cemented tungsten carbide, to form a cutting structure. PCD comprises a polycrystalline mass of diamonds that are bonded together to form an integral, tough, high-strength mass or lattice. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired. For use in the oil industry, PCD cutting elements are provided in the form of specially designed cutting elements such as PCD wafers that are configured for attachment with a subterranean drilling device.
A PDC cutter may be formed by placing a cemented carbide substrate into the container of a press. A mixture of diamond grains or diamond powder and catalyst binder is placed atop the substrate and treated under high pressure high temperature (HPHT) conditions. In doing so, metal binder (often cobalt) migrates from the substrate and passes through the diamond grains to promote intergrowth between the diamond grains. As a result, the diamond grains become bonded to each other to form the diamond layer, and the diamond layer is in turn bonded to the substrate. The substrate often includes a metal-carbide composite material, such as tungsten carbide. The deposited diamond layer is often referred to as the “diamond table” or “abrasive layer.” The term “particle” refers to the powder employed prior to sintering a superabrasive material, while the term “grain” refers to discernable superabrasive regions subsequent to sintering.
Generally, PCD may include from 85 to 95% by volume diamond and a balance of the binder material, which is present in PCD within the interstices existing between the bonded diamond grains. Binder materials used for forming conventional PCD include metals from Group VIII of the Periodic table, such as cobalt, iron, or nickel and/or mixtures or alloys thereof, with cobalt being the most common binder material used. However, while higher metal content increases the toughness of the resulting PCD material, higher metal content also decreases the PCD material hardness, thus limiting the flexibility of being able to provide PCD coatings having desired levels of both hardness and toughness. Additionally, when variables are selected to increase the hardness of the PCD material, brittleness also increases, thereby reducing the toughness of the PCD material.
FIG. 1 schematically illustrates a microstructure of a conventional PCD material 100. As illustrated, PCD material 100 includes a plurality of diamond grains 120 that are bonded to one another to form an intercrystalline diamond matrix first phase. The catalyst/binder material 140, e.g., cobalt, used to facilitate the diamond-to-diamond bonding that develops during the sintering process, is dispersed within the interstitial regions formed between the diamond matrix first phase. Particularly, as shown in FIG. 1, the binder material 140 is not continuous throughout the microstructure in the PCD material 100. Rather, the microstructure of the PCD material 100 may have a uniform distribution of binder among the PCD grains. Thus, crack propagation through conventional PCD material will often travel through the less ductile and brittle diamond grains, either transgranularly through diamond grain/binder interfaces 150, or intergranularly through the diamond grain/diamond grain interfaces 160.